1. Field of the Invention
This invention relates to a vehicle headlamp in which light irradiation patterns of a plurality of light source units, each having a light-emitting element as a light source, are combined together to form a predetermined light distribution pattern.
2. Description of Related Art
Generally, a headlamp for a vehicle is so constructed in order to form a low-beam light distribution pattern having a cut-off line at an upper end edge thereof so that a forward visibility of the vehicle's driver can be assured as much as possible without providing glare to drivers of oncoming vehicles and others.
In recent years, vehicle headlamps employing a light-emitting element as a light source have been actively developed. In Japanese Patent Publications No. 2004-95480 and 2005-166588, there is proposed a vehicle headlamp in which the light irradiation patterns of a plurality of light source units, each having a light-emitting element as a light source, are superimposed together to form a low-beam light distribution pattern.
According to these publications, light emitted from the light-emitting element 2 used as the light source generates a small amount of heat. As shown in FIG. 12, a lens 4 and a cut-off line-forming shade 6 (which are light distribution control members forming the light unit) are formed of a synthetic resin for the purpose of achieving a lightweight design. A bracket 1 (serving as a unit support member), on which the light-emitting element 2 (the light source) is mounted, is formed by a metal diecast product of good thermal conductivity in order to suppress a temperature increase that would lead to a shortened lifetime, such as reduction of the light emitted by the light-emitting element 2 and a change in luminescent color.
The lens 4 and the shade 6 are connected together by welding or adhesive bonding, and the shade 6 and the bracket 1 are fastened together by a metal fastening screw 8. A bracket 7a of a reflector 7 and a bracket 6a of the shade 6 are both fastened to the bracket 1 by the fastening screw 8.
In this kind of headlamp, light irradiation patterns, formed respectively by the plurality of light source units, are superimposed together to form a low-beam light distribution pattern. Therefore, positional accuracy (light distribution accuracy for each light source unit) between the lens 4 and the shade 6 (which are the light distribution control members) is naturally required, and the positional accuracy of the light distribution control members (the lens 4 and the shade 6) relative to the bracket 1 is also required. Namely, it is necessary that the optical axes of the light source units should be properly arranged.
Therefore, a positioning projection 6b is formed on an abutment surface of the shade 6 for abutting against the bracket 1. With this construction, the positional accuracy of the light distribution control members relative to the bracket 1 is assured.
The lens 4 and the shade 6 (the light distribution control members) are both made of a synthetic resin, and therefore can be precisely integrally connected together by welding or adhesive bonding (that is, the light distribution accuracy for each light source unit can be secured). With respect to the positional accuracy of the resin light distribution control members (the lens 4 and the shade 6) relative to the metallic bracket 1, it is preferred to fasten the shade 6 and the bracket 1 together with a suitable fastening force so that the shade 6 will not shake relative to the bracket 1. However, when the fastening force is increased in order to enhance the positional accuracy, there has been a problem that the positioning projection 6b is plastically deformed (buckled), and the positional accuracy is lowered.
In the process of developing structures for screw-fastening the resin shade 6 and the bracket 1 together, there has been proposed one structure in which a screw passage hole is formed through the metal bracket 1, and a metal fastening screw (including a taping screw) is threaded (or screwed) into a fastening portion of the resin shade 6 for the bracket 1 from a rear side (the right side in FIG. 12) of the bracket 1, as in an embodiment of the present invention, thereby fastening the shade 6 to the bracket 1. In this case, when the screwing fastening force is too large, a screw hole (screw threading portion), formed in the fastening portion of the shade 6 for the bracket, and the positioning projection are plastically deformed (buckled). As a result, there have been encountered new problems that the satisfactory positional accuracy of the light distribution control members (the lens 4 and the shade 6) relative to the bracket 1 is not obtained (that is, the optical axes of the light source units are not properly arranged) and that the screw threading portion is plastically deformed (that is, becomes loosened) by a creep phenomenon in an environment in which a change in the ambient temperature is large, so that the optical axis deviates from a proper direction.
Therefore, the inventor of the present invention considered that the plastic deformation (buckling and looseness) of the fastening portion (the screw threading portion and the positioning projection) of the shade for the bracket is attributable to the fact that the screw threading portion and the positioning projection can not withstand the fastening force because they are made of the resin. The inventor further considered that when the screw threading portion and the positioning projection are made of metal and are integrally formed with the resin shade, the fastening portion (the screw threading portion and the positioning projection) will not be subjected to plastic deformation, thus securing the positional accuracy of the light distribution control members relative to the bracket, and that the positional accuracy between the lens and the shade (which are the light distribution control members) will not be affected since that portion of the shade which is connected to the lens is made of the resin. Therefore, the inventor has constructed an experimental shade, has reviewed advantageous effects of this shade, and has confirmed that this shade is effective. Therefore, the present application has been filed.